Engine mods
05-04-2008, 09:04 PM
#1
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Engine mods
I have a 2005 GMC 2500hd. About a mouth ago I did some engine work. The truck is lifted with 35inch tires and 456 gears. I bought a comp cam kit witch included cam,pushrods,springs,retainers and 1.85 rockers. Also put on underdrive pullys,electric fans,aem intake,jba headers,gutted the cats and exhaust. I also took off the sceen from infront of the mass air sensor. I have had the truck at two different dyno tuners. Both times the truck would run good for a day then would loose power. Now the truck is running,but it feels like somthing is holding it back. The truck ran better and faster stock. Please Help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
05-05-2008, 10:07 AM
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+1....get new mass air flow/ and get new tune...its probably bogging down due to the mass air screen being off, and id you dont have a tune its hurting your performance gains
05-05-2008, 10:17 AM
#7
Also bolt on your stock pulley setup. Running underdrive pullies with an electric fan is putting a huge strain on your alternator. Going back to the stockers will lessen the load placed on your alternator.
And this is a +4 on the screen. Ebay has them for a few bucks.
Are the screens restrictive?
Absolutely they are, but by design. Is your voltage regulator restrictive? Is your air cleaner restrictive? Is your fuel filter restrictive? Are your fuel injectors restrictive? Is your fuel pressure regulator restrictive? Yes they are.....by design. Would you remove your air cleaner or fuel filter? We are blessed with the common sense that although restrictive we find these components necessary for proper operation and to remove them would be foolish or asking for trouble. It is very unfortunate that we don't possess the same common sense regarding the MAF sensor.
Understand two terms first of all. Turbulent Airflow and Laminar Airflow. They are opposites. Without definition we can identify with "turbulent" but "laminar" airflow would define as "smooth, straightened out, regulated".
To help understand some conflicting articles I will point out an important factor here right away. There is no such thing as turbulence free airflow. Airflow is a "fluid flow" and a fluid flowing past obstructions, against boundaries, even the composition of the fluid itself in different densities and pressures create turbulence that can't be removed. So when we speak of Laminar Airflow being smoothed out and being the opposite of turbulent airflow we're speaking of a "controlled turbulence" vs. "uncontrolled turbulence".
Envision this process by thinking of your kitchen faucet. The little screen on the end. Take it out and watch your water flow increase but also notice it splash around and surge. You can see the uneven flow very easily. Put the aerator back in and see it smooth out in a more regulated even flow. Look at the end of most hair dryers and they will have a screen in them. Of course this is to prevent getting your hair sucked up in there and catching your head on fire BUT it also disperses the air in a more even, regulated pattern. Think of the construction of a dam on a river. You KNOW it is restrictive. It "holds back" the natural flow of water and regulates it to a desired given amount. Why? To do something productive with the process of flow. Just like your MAF screens.
I'll chop this section down to the most basic of processes. GM didn't invent this process, as a matter of fact it is the same process used by the weather industry to measure "chill factor" so it's theory was utilized by GM not invented by them.
1. You have a small wire inside your MAF which can be heated.
2. It is calibrated at zero airflow to be a certain temperature.
3. Air flowing across the wire cools it off. The more air flow the cooler the wire.
4. A voltage is supplied to that wire to keep it at a constant temperature. The more air flowing, the cooler the wire, the more voltage required to keep it the same temp.
5. This voltage fluctuation is a measurable, readable function which when converted to a digital output can be used for calibrations of airflow entering your intake.
6. These calibrations are referenced to a lookup table stored in your ECM and based on these fluctuations various functions of your engine are controlled based on the amount of airflow you are encountering.
The screens are there simply to provide a steady, stable, regulated environment for the most precise calculations available. Now with that I ask: Would it be easier to count the number of gallons that flow past a certain point in the river ...with the dam or without it? That is what your screens are for... to establish "near as possible" level playing field ground zero reference point for calibrations.
What Happens When They are Removed?
Without the screen, the computer can not take a correct reading on how much air is entering the engine. When you port the MAF housing and/or remove the screens you are causing air to move by the sensors that is not being measured. Lower frequency outputs are being read by the lookup charts and the calculations are based on lower than actual airflow.
This makes the ECM lean out the fuel mixture, add timing, then cannot determine load changes properly, which could lead to transmission problems. Since it cannot determine proper load changes, shift points are moved around which could lead to tranmission failure.Then the oxygen sensors read the lean fuel mixture and bump it back up to compensate for the MAF sensors low readings.
In Summary I would say that I have heard of people making this mod and not having trouble codes. I have also heard of reported gains in performance. In both of these situations, if true, you have my respect and congratulations but I have never seen proof of these gains especially on a stock setup. I have however lost count of the number of post that are encountering trouble after making this "free" mod. Further I would say that if the horsepower is not there in the first place you're sure not going to create any new horsepower cutting out your screens. And without proper tuning change you can create more problems than whatever gains you may see.
The MAF is a truly unique and awesome device that allows us to drive in different environments (altitudes) with no intake modifications. Allows us to make "other" performance mods without having to calibrate a new PROM. To butcher it and make it less accurate and precise just doesn't make sense to me.
1. If you are driving a stock intake car this mod will do absolutely nothing for you.
2. If you have such a heavily modified engine that it would make a difference Why are you using the MAF system anyway? .....you should be on Speed Density with a custom tune.
And this is a +4 on the screen. Ebay has them for a few bucks.
Are the screens restrictive?
Absolutely they are, but by design. Is your voltage regulator restrictive? Is your air cleaner restrictive? Is your fuel filter restrictive? Are your fuel injectors restrictive? Is your fuel pressure regulator restrictive? Yes they are.....by design. Would you remove your air cleaner or fuel filter? We are blessed with the common sense that although restrictive we find these components necessary for proper operation and to remove them would be foolish or asking for trouble. It is very unfortunate that we don't possess the same common sense regarding the MAF sensor.
Understand two terms first of all. Turbulent Airflow and Laminar Airflow. They are opposites. Without definition we can identify with "turbulent" but "laminar" airflow would define as "smooth, straightened out, regulated".
To help understand some conflicting articles I will point out an important factor here right away. There is no such thing as turbulence free airflow. Airflow is a "fluid flow" and a fluid flowing past obstructions, against boundaries, even the composition of the fluid itself in different densities and pressures create turbulence that can't be removed. So when we speak of Laminar Airflow being smoothed out and being the opposite of turbulent airflow we're speaking of a "controlled turbulence" vs. "uncontrolled turbulence".
Envision this process by thinking of your kitchen faucet. The little screen on the end. Take it out and watch your water flow increase but also notice it splash around and surge. You can see the uneven flow very easily. Put the aerator back in and see it smooth out in a more regulated even flow. Look at the end of most hair dryers and they will have a screen in them. Of course this is to prevent getting your hair sucked up in there and catching your head on fire BUT it also disperses the air in a more even, regulated pattern. Think of the construction of a dam on a river. You KNOW it is restrictive. It "holds back" the natural flow of water and regulates it to a desired given amount. Why? To do something productive with the process of flow. Just like your MAF screens.
I'll chop this section down to the most basic of processes. GM didn't invent this process, as a matter of fact it is the same process used by the weather industry to measure "chill factor" so it's theory was utilized by GM not invented by them.
1. You have a small wire inside your MAF which can be heated.
2. It is calibrated at zero airflow to be a certain temperature.
3. Air flowing across the wire cools it off. The more air flow the cooler the wire.
4. A voltage is supplied to that wire to keep it at a constant temperature. The more air flowing, the cooler the wire, the more voltage required to keep it the same temp.
5. This voltage fluctuation is a measurable, readable function which when converted to a digital output can be used for calibrations of airflow entering your intake.
6. These calibrations are referenced to a lookup table stored in your ECM and based on these fluctuations various functions of your engine are controlled based on the amount of airflow you are encountering.
The screens are there simply to provide a steady, stable, regulated environment for the most precise calculations available. Now with that I ask: Would it be easier to count the number of gallons that flow past a certain point in the river ...with the dam or without it? That is what your screens are for... to establish "near as possible" level playing field ground zero reference point for calibrations.
What Happens When They are Removed?
Without the screen, the computer can not take a correct reading on how much air is entering the engine. When you port the MAF housing and/or remove the screens you are causing air to move by the sensors that is not being measured. Lower frequency outputs are being read by the lookup charts and the calculations are based on lower than actual airflow.
This makes the ECM lean out the fuel mixture, add timing, then cannot determine load changes properly, which could lead to transmission problems. Since it cannot determine proper load changes, shift points are moved around which could lead to tranmission failure.Then the oxygen sensors read the lean fuel mixture and bump it back up to compensate for the MAF sensors low readings.
In Summary I would say that I have heard of people making this mod and not having trouble codes. I have also heard of reported gains in performance. In both of these situations, if true, you have my respect and congratulations but I have never seen proof of these gains especially on a stock setup. I have however lost count of the number of post that are encountering trouble after making this "free" mod. Further I would say that if the horsepower is not there in the first place you're sure not going to create any new horsepower cutting out your screens. And without proper tuning change you can create more problems than whatever gains you may see.
The MAF is a truly unique and awesome device that allows us to drive in different environments (altitudes) with no intake modifications. Allows us to make "other" performance mods without having to calibrate a new PROM. To butcher it and make it less accurate and precise just doesn't make sense to me.
1. If you are driving a stock intake car this mod will do absolutely nothing for you.
2. If you have such a heavily modified engine that it would make a difference Why are you using the MAF system anyway? .....you should be on Speed Density with a custom tune.
Last edited by InchUp; 05-05-2008 at 10:36 AM. Reason: Spelling while hung over sucks lol